Preliminary Servicing & Stormwater Management Report

Transcription

1 Prepared By: Hart Subdivision, City of Guelph Preliminary Servicing & Stormwater Management Report GMBP File: May 22, 2015 GUELPH OW EN SOUND LISTOW EL KITCHENER EXETER HAMILTON GTA 650 W OODLAW N RD. W., BLOCK C, UNIT 2, GUELPH ON N1K 1B8 P:

2 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 TABLE OF CONTENTS 1.0 INTRODUCTION LOCATION EXISTING CONDITIONS Land Use Topography Soils Groundwater PROPOSED DEVELOPMENT Site Grading Streets Harts Lane Water Supply Sanitary Sewer Storm Sewer Foundation Drainage Stormwater Management STORMWATER MANAGEMENT CRITERIA STORMWATER MANAGEMENT PLAN Pre-Development Conditions Post-Development Conditions Stormwater Management Overview Lot Level Controls Conveyance Controls Site Plan Controls Stormwater Management Facility Preliminary Overall Grading Water Budget SEDIMENT AND EROSION CONTROL PLAN CONCLUSIONS I

3 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 APPENDICES APPENDIX A: HARTS LANE DESIGN OPTIONS APPENDIX B: STORMWATER MANAGEMENT ANALYSIS PRE-DEVELOPMENT CONDITIONS APPENDIX C: STORMWATER MANAGEMENT ANALYSIS POST-DEVELOPMENT CONDITIONS APPENDIX D: OIL/GRIT SEPARATOR DESIGN SUMMARY APPENDIX E: PERMEAMETER TEST AND GEOTECHNICAL REPORT V.A. WOOD APPENDIX F: MOE INTREPRETATION BULLETIN FEBRUARY Preliminary Grading Plan 1 LIST OF DRAWINGS 2. Preliminary Grading Plan 2 3. Preliminary Servicing Plan 3 4. Preliminary Servicing Plan 4 LIST OF FIGURES Page 1. Key Map Draft Plan of Subdivision Pre-Development Drainage Area Plan Post-Development Drainage Area Plan Enhanced Infiltration Structure Details Stormwater Management Facility Typical Section x 1800 Outlet Structure Details x 2400 Outlet Structure Details Pre Development Watershed Plan Post Development Watershed Plan Post Development Model Schematic... Appendix C 12. Oil/Grit Separator Drainage Areas... Appendix D II

4 PEOPLE ENGINEERING ENVIRONMENTS HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMWATER MANAGEMENT REPORT MAY, 2015 GMBP FILE: INTRODUCTION In response to the engineering comments provided by the GRCA on July 31, 2014 and the City of Guelph on December 5, 2014 this report has been revised to support the Draft Plan of Subdivision and Zone Change Application on Part of Lot 4 Concession 7, City of Guelph herein after referred to as the Hart Subdivision, GM BluePlan Engineering Limited has prepared this report to address the servicing and stormwater management requirements for the development. 2.0 LOCATION The proposed subdivision development is located on the southeast corner of the intersection of Kortright Road and Rickson Avenue in the City of Guelph. The site boundaries include existing residential development (fronting onto Kortright Road West, Darnell Road and Rickson Avenue) to the north, south and west, and a wetland area to the east. Figure 1 shows the location of the proposed development and the surrounding area. PAGE 1 OF 26

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6 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, EXISTING CONDITIONS 3.1 Land Use The subject property, outside of the wetland, is currently used for residential and ongoing agricultural activities. Ground cover consists of actively cropped fields with some trees, shrubs and lawns around the existing house. The eastern portion of the property is adjacent to a GRCA regulated wetland. 3.2 Topography The site currently slopes towards the existing wetland located at the easterly boundary of the site with gradients ranging from 3.5 to 10% with an average of 4.3%. Runoff drains overland towards the wetland area adjacent to the eastern site boundary. 3.3 Soils The predominant surface soil type throughout the site is a Guelph Loam with areas of Much and Gilford Loam (Ontario Soil Surveys, Report No. 35, Wellington County). A BC hydrologic soil classification is used for the site. A geotechnical investigation was prepared by V.A. Wood Inc. in March The subsurface soils consist of compact to very dense silty sand, sand and silt and clayey sandy silt till with poor drainage characteristics. A copy of the geotechnical investigation is attached in Appendix D. 3.4 Groundwater A Hydrogeological Study is being completed concurrently with this Servicing Study in support of the Draft Plan application. The Hydrogeological Study is submitted under separate cover. Please see the Hydrological Study for details regarding the installation of piezometers and monitoring wells for the site. PAGE 2 OF 26

7 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, PROPOSED DEVELOPMENT The Draft Plan of Subdivision (Figure 2) illustrates the proposed lot fabric, stormwater management area, park block and internal roads. The proposed subdivision consists of single family homes, semi-detached homes, a townhouse block, and an apartment block. Access to the subdivision will be with street connections to Carrington Drive and Rodgers Road. The draft plan includes a block to provide the City with the opportunity of providing servicing, a walkway and/or a road connection to Harts Lane. A conceptual servicing figure (Drawings 3 and 4) shows how the municipal services can be extended to service the proposed development. 4.1 Site Grading The site layout for the stormwater management area and the internal roads are shown on the Preliminary Grading Plans (Drawings 1 and 2). The grade and elevation of the internal streets are determined by the elevation of the proposed stormwater management facility and the existing farmhouse building. The major overland flow for the townhouse block and the single family lots will be conveyed through the municipal right of ways to the proposed stormwater management facility located at the southeast corner of the property, eventually discharging into the southerly portion of the wetland. The major overland flow from the park and apartment blocks will be conveyed to the northerly portion of the wetland. The proposed residential units have be graded as split drainage, walk-outs and back to front draining lots to work with the existing topography. 4.2 Streets All streets will be constructed to City of Guelph standards as follows: With an urban road cross-section having a 17 metre right-of-way width. With concrete curb and gutter and asphalt on the 8.8 metre wide travelled portion of the road. With minimum slopes of 0.5% and maximum slopes of 8.0%. With a 1.5 metre wide concrete municipal sidewalk on one side of each street, approximately 2.3 metres behind the curb. The development includes connections to Rodgers Road and Carrington Drive. To conform to the intent of the Community Trail Network, the combination of sidewalk and trails within the proposed development will provide the opportunity for north-south pedestrian and bicycle access between Edinburgh Road along Carrington Drive to Kortright Road and west-east pedestrian and bicycle access along Harts Lane to Gordon Street. PAGE 3 OF 26

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9 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, Harts Lane Harts Lane is an existing 20 metre wide municipal road allowance that terminates the easterly boundary of the subject property. An existing 5.2 m wide farm lane extends from the easterly boundary of the subject property across the wetland on the municipal road allowance to the portion of Harts Lane built as a rural municipal road on the easterly side of the wetland. The Hart Farm Property Traffic Impact Study by Paradigm Transportation Solutions Limited concludes that the Harts Lane connection is not required to improve the operation of the study area intersections. Four options were considered in the re-development of Harts Lane. The options are summarized in Appendix A of this report. From consultation with the City of Guelph, Option 1 is preferred; retain Harts Lane as a multi-use trail connecting the proposed subdivision to the developed portion of Hart s Lane. A cul-de-sac turnaround is proposed on the easterly side of the wetland at the terminus of the existing Harts Lane municipal road. This option following existing topography, does not require grading into the wetland and allows the City to install sanitary and water mains under the wetland by trenchless methods. 4.4 Water Supply The proposed development will be serviced via a 200 mm diameter watermain with connections to the existing 250 mm diameter watermain on Carrington Drive and the existing 150 mm diameter watermain on Rodgers Road to create a looped system. Hydrants located throughout the subdivision as per the City of Guelph Specifications will provide fire protection. 4.5 Sanitary Sewer It is the City s intent to connect an existing 300 mm diameter sanitary sewer stub located on Harts Lane, to the east of the wetland, to the existing 375 mm sanitary trunk sewer located on Carrington Drive near the southerly edge of the proposed subdivision. A future extension of the 375 mm diameter sanitary trunk sewer will be constructed within the Harts Lane right of way. Due to the depth required for the installation of the 375 mm diameter trunk sewer (between 6 and 8 metres) within the subdivision lands, the subdivision will be serviced by a proposed local 200 mm diameter sanitary sewer installed at standard depths in parallel with the 375 mm diameter trunk sewer. The development of the Hart Subdivision will extend the 375 mm diameter trunk sewer to Harts Lane on the westerly side of the wetland for future extension to the east. 4.6 Storm Sewer The local storm sewer system within the proposed development will be sized to convey the runoff from a 5-year design storm to the stormwater management facility. PAGE 4 OF 26

10 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 Major storm runoff will be conveyed through the street right-of-ways, ultimately discharging to the proposed stormwater management facility and the existing wetland. 4.7 Foundation Drainage The foundation drainage will be provided through sump pits and pumped to grade towards rear yard areas. This will increase the travel path, promoting on site infiltration/recharge. 4.8 Stormwater Management A description of the stormwater management system appears in Section 6.0 of this report. PAGE 5 OF 26

11 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, STORMWATER MANAGEMENT CRITERIA The studies, policies and guidelines used to develop the stormwater management plan are as follows: 1) The Stormwater Management Practices Planning and Design Manual, ) Stormwater Management Planning and Design Manual, ) CVC, TRCA Low Impact Development Stormwater Management Planning and Design Guide, ) The Interim Stormwater Quality Control Guidelines, ) The Stormwater Quality Best Management Practices Manual, ) The MTO Drainage Management Technical Guidelines, ) The Ontario Urban Drainage Design Guidelines, 1987 The objectives of the stormwater management plan are as follows: a) Provide quantity control to attenuate the rate of post-development stormwater runoff to the pre-development flow rates for the 5 and 100 year design storms. b) Provide enhanced (80% TSS removal) water quality control prior to discharge from the site. c) Attenuate rainfall runoff from the 4 hour 25mm storm event and release it over a minimum period of 24 hours. d) Maintain, as much as feasible, the recharge and runoff patterns of the pre-development site. The parameters used to evaluate and design the stormwater management plan is as follows: City of Guelph rainfall parameters were used to generate the mass rainfall data required to model the 25 mm, 5 year and 100 year design storms. The Chicago storm parameters and the total depth of rainfall for each storm are as follows: 25 mm 2 Year 5 Year 100 Year a = b = c = r = t d = Rainfall depth (mm) The SCS (Soil Conservation Service) infiltration method was used in the runoff calculations. From the Ontario Soil Surveys, Report No. 35, Wellington County, the majority of the soils on site are Guelph Loam with a hydrologic classification of BC, and parts of Muck and Gilford Loam with a hydrologic classification of B. The overall hydrologic soil classification for the site is BC. PAGE 6 OF 26

12 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 SCS infiltration parameters for a hydrologic type BC soil have been used in the analysis of the stormwater management system. The infiltration parameters used are as follows: Land Use Curve Number Parkland 74 Agricultural 78 Residential Lawns 74 Impervious/roofs 98 The hydrologic modeling software, MIDUSS, was used to create the runoff hydrographs and to route the flows through the storage and channel structures. PAGE 7 OF 26

13 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, STORMWATER MANAGEMENT PLAN 6.1 Pre-Development Conditions Under existing conditions, there are no defined conveyance systems within the development site directing flows to specific outlets. In the event of a rainfall significant enough to generate flows leaving the site, runoff flows overland towards the existing wetland located at the easterly property boundary. Under existing conditions, the overall site was analyzed as three (3) drainage catchments. The catchment numbers and their respective drainage areas are illustrated in Figure 3. The pre-development flow rates and runoff volumes from the site are summarized in Table No. 1. The existing conditions hydrologic modelling is included in Appendix B. Table 1: Pre-Development Peak Flow Rates and Runoff Volumes from Site 2 Year Catchment 100 Catchment 200 Catchment 300 Total Wetland Total Site Flow Rate (m 3 /s) Runoff Volume (m 3 ) Year Flow Rate (m 3 /s) Runoff Volume (m 3 ) Year Flow Rate (m 3 /s) Runoff Volume (m 3 ) 369 1,678 2,787 4,465 4,834 PAGE 8 OF 26

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15 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, Post-Development Conditions Under post-development conditions, the overall development has been divided into four (4) drainage catchments. The catchment numbers and their respective drainage areas are illustrated in Figure 4. The post development percent impervious for each catchment is calculated based on the City of Guelph Runoff Coefficient to Percent Impervious Conversion Table (Table 2) and the equation below. I = (. ). Where: I = % Impervious C = Runoff Coefficient Table 2: Runoff Coefficient C to Percent Impervious Conversion Land Use Runoff Coefficient Percent Impervious Parks (> 4-ha) Parks (< 4-ha) Single Family Residential (> 18m Frontage) Single Family Residential (12-18m Frontage) Single Family Residential (< 12m Frontage) Semi-detached Maisonettes, townhouses, etc Apartments Schools Churches Industrial Commercial, Highway Commercial Heavily Developed Areas PAGE 9 OF 26

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17 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 The percent impervious for each catchment under post-development conditions is calculated in Table 3. Table 3: Percent Impervious Calculation Type Area (ha) Runoff Coefficient "C" % Impervious Catchment 100 Wetland Buffer % Catchment 101 Apartment Block % Catchment 102 Park Block % Catchment 200 Townhomes % Semi-Detached % Ex-House % Single Family 13.7 m wide lots % m wide lots % 11.2 m wide lots % 9 m wide lots % Roads % City Block % SWM Facility % Total % PAGE 10 OF 26

18 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, Stormwater Management Overview A treatment train approach, consisting of lot level, conveyance and end-of-pipe management practices, is proposed to filter and remove sediments from the storm runoff prior to discharging it to the existing wetland. Lot level controls will include directing roof leaders to grassed rear yard areas and rear yard swales. The runoff from the roof and rear yard areas will be filtered through the grassed yards and swales prior to discharging to rear lot catch basins and conveyance by the storm sewer system to the stormwater management facility. Conveyance controls will include regular maintenance of the storm sewer system including cleaning of manholes, catch basins and oil/grit structures to remove sediments. Quality control will be provided by installing a series of oil/grit separators prior to discharging to the proposed stormwater management facility and the wetland. The end-of-pipe component for the single family and townhome blocks consists of a stormwater management wetland facility designed to provide water quality and quantity controls. The facility will be designed to provide a 24 hour attenuation period for the 25mm design storm event. The outlet structure will provide quantity controls to limit post-development flow rates to less than or equal to the existing flow rates. The apartment block will have its own stormwater management system which will be design at the site plan approval stage. The stormwater management system may consist of rooftop attenuation, rain gardens or parking lot storage complete with an oil/grit separator for quality control. The stormwater management pond and apartment block stormwater management system will discharge to individual energy dissipation structures to cool and spread the storm discharge over a broad area along the wetland interface avoiding a point source discharge. Enhanced LID Infiltration structures are proposed throughout the site to maintain or exceed predevelopment infiltration rates. These structures will be explained in greater detail in Sections 6.4 and Lot Level Controls Stormwater management practices recommended for providing lot level controls on this site are as follows: a) Roof Drainage to Ground Surface The driveways and the front yards will drain to the street. The roof and rear yard will generally drain to the rear of the lot. The roof runoff will be filtered across the grassed surface. The runoff for any event large enough to generate flow to the swale system will be adequately filtered by the grass. PAGE 11 OF 26

19 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 b) Rear Yard Swales The grading of the lots will be to current City of Guelph standards with minimum slopes of 2%. Where practical, the length of the rear lot swales between catch basins will be increased to extend the contact time with the grassed surfaces. To promote water retention on the lots and in the swales, it is recommended that the average depth of graded topsoil be 300 mm. c) Low Impact Development Techniques Low Impact Development techniques are proposed to function in accordance with the CVC/TRCA Low Impact Development Stormwater Management Planning and Design Guide, MOECC Interpretation Bulletin 2015 and the MOE Stormwater Management Planning and Design Manual The MOECC Interpretation Bulletin outlines the suitability of LID infiltration facilities for quantity control purposes in native soils with percolation rates less than 15 mm/hr as long as the facilities can be sized so that they empty between events. Please see Appendix F for a copy of the MOECC Interpretation Bulletin. A typical storm event occurs every 24 to 72 hours. Therefore the required draindown time for an infiltration structure to comply with MOECC guidelines for stormwater management purposes is 24 to 48 hours. Draindown Time Calculations: A Guelph Permeameter Test was completed by V.A. Wood Inc. in September Please see Appendix D. Based on the test results, the sand and silt, some clay, trace gravel soil layer has a hydraulic conductivity of 3.04 x 10-6 cm/s. From Figure C1 of the Low Impact Development Planning and Design Guide, the percolation rate is 12 mm/hr. From Table C2, the safety factor can range from 2.5 to 3.5 depending on the depth of the underlying soil. We will assume a best case scenario of 2.5. Therefore the design percolation rate is 4.8 mm/hr. Infiltration parameters for a typical lot are examined. Given the lot dimensions of 11.2 m x 32 m and approximate house dimensions of 9.2 m x 18.5 m, the runoff volume generated under the 25 mm design storm is as follows: V = m x 9.2 m x 18.5 m = 4.3 m 3 Providing a drywell that is 1.2 m deep by 1.2 m wide by 9 m long (1/3 void ratio) of 19 mm clear stone, the storage volume is 4.3 m 3 and the effective contact area is 32.4 m 2. PAGE 12 OF 26

20 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 Using MOE SWM Planning and Design Manual Equation 4.3, =, t = Where A = contact area of trench (32.4 m 2 ) V = runoff volume to be infiltrated (4.3 m 3 ) P = percolation rate of surrounding native soil (4.8 mm/hr.) n = porosity of the storage media (1/3 for 19 mm clear stone) t = retention time (24 to 48 hours MOE requirement) t = (. ) (. )(. )(. ) t = 92 hours (3.86 days) The drain down time for the infiltration structure would be approximately 92 hours exceeding the drain down of 24 to 48 hours required by the MOECC for stormwater management purposes. Enhanced Infiltration and Ground Water Recharge: Given that a typical lot level LID infiltration structure cannot meet the draindown time requirements for stormwater management purposes, we are proposing the use of LID infiltration structures strictly for groundwater recharge enhancement to maintain the natural hydrologic cycle of the site. The volume infiltrated through the enhanced LID infiltration structures between storm events is not used in the stormwater management calculations for the site. The proposed enhanced LID infiltration structures are to be installed in front and back yard areas of the single family homes located within Catchment 200. The apartment Block, Catchment 101 will have its own enhanced LID infiltration structure that will collect and infiltrate the roof water. Figure 5 illustrates the location of the infiltration structures for the site. Each enhanced LID infiltration structure will have an overflow connection to the storm sewer in case the water level reached the top of the structure. Catchment Enhanced LID Infiltration Structure Recharge Potential: A total of m 3 of enhanced recharge volume potential on an event basis is available from the enhanced LID infiltration structures in Catchment 200. Based on approximately 94.6 discharge events per year (365/3.86) and multiplying by the infiltration volume of m 3, the potential maximum annual enhanced recharge volume is approximately 32,697 m 3 if the structures are always full (Table 18, Section 6.9). Given the current monthly variation for precipitation in the City of Guelph, Table 18 in Section 6.9 calculates the maximum recharge potential of the enhanced infiltration structures on a monthly basis and the available enhanced recharge volume based on the City s monthly PAGE 13 OF 26

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22 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 average precipitation values. The annual infiltration volume available from the enhanced LID infiltration structures is 11,150 m 3. Section 6.9 of this report combines the infiltration volume from the enhanced LID infiltration structures with the natural recharge infiltration volume of the site to calculate the water balance of the site on a monthly and yearly basis. Catchment Enhanced LID Infiltration Structure Recharge Potential: A total of 51.3 m 3 of enhanced recharge volume potential on an event basis is available from the enhanced LID infiltration structure in Catchment 101. Based on approximately 59.4 discharge events per year (365/6.14) and multiplying by the infiltration volume of 51.3 m 3, the potential maximum annual enhanced infiltration volume is approximately 3,053 m 3 if the structures are always full (Table 15, Section 6.9). Given the current monthly variation for precipitation in the City of Guelph, Table 15 in Section 6.9 calculates the maximum recharge potential of the enhanced infiltration structure on a monthly basis and the available enhanced recharge volume based on the City s monthly average precipitation values. The infiltration volume available from the enhanced LID infiltration structures is 1,349 m 3. Section 6.9 of this report combines the infiltration volume from the enhanced LID infiltration structures with the natural recharge infiltration volume of the site to calculate the water balance of the site on a monthly and yearly basis. 6.5 Conveyance Controls Conveyance controls will be achieved mainly through municipal maintenance of the storm sewer system. The regular cleanout of the manholes, catch basins and oil/grit structures will remove the heavier sediments deposited from the runoff during storm events. PAGE 14 OF 26

23 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, Site Plan Controls The apartment block will require its own stormwater management system complete with quality controls which will be designed at the site plan approval stage. Preliminary analysis estimates that approximately 315 m 3 of storage is required to attenuate post development flows. The apartment block stormwater management system may consist of rooftop attenuation, bioretention facilities, rain gardens or parking lot storage, all of which will be designed at the site plan approval stage in accordance to the guidelines, policies and procedures in place at the time of design. The apartment block will require an enhanced infiltration structure that has a storage volume of 51 m 3 and a contact area of 242 m 2 in order to meet the enhanced infiltration volume outlines in Sections 6.4 and 6.9 of this report. Table 4 illustrates the preliminary design of a storage system for the apartment block. Table 4: Apartment Block Stage/Storage/Discharge Catchment 101 CONTROL Peak Flow m³/s Available Capacity Storage Volume m³ Storage Elevation m Invert Peak Flow m³/s Actual Capacity Used Storage Volume m³ Storage Elevation m 2 year Obvert year Top of Grate Weir year Overflow Quality control for the apartment block can be achieved through an oil/grit separator such as a Stormceptor STC 2000 unit removing 80% of the total suspended solids while treating 93% of the runoff volume. Flows discharged from the proposed Apartment Block stormwater management facility will be routed over a 40 m long energy dissipation structure which will cool the runoff and will provide a continuous linear discharge area versus a point discharge. PAGE 15 OF 26

24 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, Stormwater Management Facility The end-of-pipe component consists of a stormwater management pond, located at the southeast corner of the site. The proposed stormwater management facility is designed to accept and control flows from the townhouse and single family blocks (Catchment 200). Further details of the water quality and quantity controls for the proposed stormwater management pond are discussed in the following sections. a) Water Quality Pre-treatment of stormwater runoff discharging to the stormwater management facility will be provided by two (2) oil/grit separator structures. Please refer to Figure 12, Appendix D for the oil/grit structure catchments areas. Stormwater pre-treatment for Catchments A and B (from Figure 12), the single family and townhome blocks, is provided by two oil/grit separators such as Stormceptor STC 9000, removing 81 % of total suspended solids while treating 94% of the runoff volume. This pre-treatment of the stormwater runoff from the development will reduce the frequency that the stormwater management pond will require remediation from sediment buildup. Pretreatment will remove larger sediments before they are deposited within the stormwater management pond facility. Oil/grit separator sizing is included in Appendix D. The stormwater management facility has been designed to function as a wetland. From Interpolating Table 3.2 of the Stormwater Management Planning and Design Manual 2003 for 73% imperviousness, a wetland facility requires 124 m³/ha of storage volume to provide an enhanced level of protection. 40 m³/ha of the required storage volume is extended detention volume, while the remaining 84 m³/ha is permanent pool. The required permanent pool volume for the contributing lands, (8.45 hectares) is 710 m³. The water quality cell has been designed with shallow, 0.30 meters deep, permanent pool. The permanent pool creates approximately 770 m³ of storage. The forebay and outlet structure stilling basin contribute approximately 192 m³ and 54 m 3 of storage for a total of 1,016 m³. The forebay represents 10% of the total permanent pool area which is acceptable by MOE requiring a maximum of 20%. The forebay and outlet structure stilling basin surface area represent about 15% of the total permanent pool area which is less than the MOE maximum of 25%. Runoff will be discharged from the proposed facility at a controlled rate. A flow splitting structure will direct a portion of the runoff to the north part of the wetland via a 300 mm diameter sewer, while the remaining runoff will discharge to the south part of the wetland via a 450 mm diameter sewer. Both north and south discharge locations have an energy dissipation structure designed to cool and spread the runoff over a wide area, eliminating a point source discharge. The energy dissipation structures will also provide a final polishing mechanism, filtering out any fine suspended solids from the runoff prior to it being discharged to the respective buffer area for conveyance to the wetland. PAGE 16 OF 26

25 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 b) Extended Detention Extended detention volume is calculated based on the runoff volume (1099 m 3 ) generated by the 4 hour 25 mm design storm event. The outlet structure has been designed to provide a 24 -hour draindown time for the 4 hour 25 mm design storm event corresponding to a peak flow rate of m³/s. From the design of the stormwater management pond, a storage volume of 1099 m³ corresponds to a ponding depth of approximately 0.36 metres. The outlet structure has been designed with a 130 mm diameter orifice, which will control the extended detention volume to the required release rate. c) Pond Routing In addition to the water quality controls, the outlet structure will provide quantity controls to limit post-development flows to less than or equal to the pre-development flow rates. The outlet structure is designed with a 130 mm diameter orifice at an elevation of m and a lip elevation of m. Please see Figures 6 and 7 for a detail of the outlet structure. A 10 m long weir is proposed at an elevation of m to allow storms greater than the 100 year design storm event to flow to the wetland at a controlled rate. Table 5 compares the routing results through the stormwater management pond with the available stage/storage/discharge capacities. Table 5: Stormwater Management Pond Stage/Storage/Discharge Capacity - Catchment 200 Control Point Available Capacities Actual Capacity Used Drain Down Peak Storage Storage Peak Storage Storage Time Flow Volume Elevation Flow Volume Elevation (hrs.) m³/s m³ m m³/s m³ m Pond Bottom mm , Year , CB Lip , Year , Year , Overflow Weir , Top of Pond , A freeboard of 0.29 m has been provided in the facility under the 100 year design storm event. PAGE 17 OF 26

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29 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 d) Sediment Forebay Design The stormwater management facility has been designed with a 1.0 m deep sediment forebay. The sediment forebay has been designed as recommended within the MOE guidelines. Table 6 summarizes the required and provided parameters within the sediment forebay design. Table 6: Sediment Forebay Design Details Forebay Dispersion Length (m) 26.0 Settling Length (m) 13.2 Flow Velocity (m/s) 0.50 Required Length to Width Ratio 2:1 Settling Velocity (m/s) Forebay Area/P.P. Area Deep Water Area/P.P Area 20% max 25% max Forebay Length (m) 27.4 Flow Velocity (m/s) 0.11 Provided Length to Width Ratio 2.7:1 Forebay Area/P.P. Area 10% Deep Water Area/P.P Area 15% The sediment forebay has been designed to provide the required dispersion and settling lengths in order to settle particulates in the forebay prior to discharge to the wetland. PAGE 18 OF 26

30 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 e) Sediment Loading and Cleanout Frequency From Table 6.3, Stormwater Management Planning and Design Manual, the annual sediment loading for a Catchment having an imperviousness value of 73% would be approximately 3.0 m³/ha. Table 7 illustrates the adjusted sediment loading due to the oil/grit separators located upstream of the pond. The sediment contribution is calculated as follows: ( ) (3.0 /h ) [1 ( %)( %)] = ( ) Table 7: Sediment Loading Analysis Catchment Area 3.0 m 3 /ha TSS Removal Volume Treated Sediment Contribution A 3.55 ha m 3 81% 94% 2.54 m 3 B 3.63 ha m 3 81% 94% 2.60 m 3 Total 5.14 m 3 The annual sediment loading to the stormwater management pond, adjusted for the oil/grit separators, is 5.14 m³. The forebay portion of the permanent pool is where most of the sediment accumulation will occur. Based on half of the 192 m 3 of storage volume being used for sediment storage, a cleanout frequency of 18 years is expected. The oil/grit separators need to be cleaned a minimum of once per year as required. f) Post Development Conditions Table 8 summarizes the post-development flow rates and volumes from all catchments Table 8: Controlled Flow Rate and Runoff Volumes All Design Storms Design Storms Total 2 Year Flow Rate (m 3 /s) Runoff Volume (m 3 ) ,885 2,181 5 Year Flow Rate (m 3 /s) Runoff Volume (m 3 ) ,507 2, Year Flow Rate (m 3 /s) Runoff Volume (m 3 ) ,972 7,253 PAGE 19 OF 26

31 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 g) Flow Diverted from Catchment 200 Flow Splitting Structure Table 9 summarized the flow volume being diverted to north and south portions of the wetland buffers by the flow splitting structure. Table 9: Flow Diverted from Catchment 200 to North and South Wetland Buffer Outlets Design Storm Runoff Volume to North Wetland (m 3 ) Runoff Volume to South Wetland (m 3 ) Total (m 3 ) 2 Year Year Year Average % 31% 69% 100% h) Comparison of Existing Conditions and Post-Development Tables 10 and 11 summarize the pre and post development flows and runoff volumes to the north and south wetland outlets. Table 10: Pre and Post-Development Flows Comparison Wetland to the north of Harts Lane Wetland to the south of Harts Lane Pre- Development 2 Year (m 3 /s) 5 Year (m 3 /s) 100 Year (m 3 /s) Post- Development Pre- Development Post- Development Pre- Development Post- Development Total PAGE 20 OF 26

32 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, 2015 Table 11: Pre and Post-Development Runoff Volume Comparison Wetland to the north of Harts Lane Wetland to the south of Harts Lane Pre- Development 2 Year (m 3 ) 5 Year (m 3 ) 100 Year (m 3 ) Post- Development Pre- Development Post- Development Pre- Development Post- Development 294 1, ,325 1,678 2, , ,620 2,787 4,329 Total 775 2,181 1,241 2,945 4,465 7,253 The 2, 5 and 100 year design storm post development flows to the north and south portion of the wetland are less than the pre development flows. Table 12 summarizes the depth of flow being released from the energy dissipation structures into the respective wetland outlets. Table 12: Flow Depth Released from the Energy Dissipation Structures into the Receiving Wetland Outlets Discharge Location Apartment Block (Catchment 101) to North portion of Wetland via Energy Dissipation Structure Catchment 200 to North portion of Wetland via Energy Dissipation Structure Catchment 200 to South portion of Wetland via Energy Dissipation Structure 2 Year Flow Depth (m) 5 Year Flow Depth (m) 100 Year Flow Depth (m) Preliminary Overall Grading Drawings 1 and 2 show the preliminary grading for the development. PAGE 21 OF 26

33 HART SUBDIVISION, CITY OF GUELPH PRELIMINARY SERVICING & STORMW ATER MANAGEMENT REPORT GMBP FILE: MAY 22, Water Budget The average annual precipitation for the area in which the study site is located is estimated to be about 923 mm. This amount is based on precipitation data recorded at the Guelph Arboretum meteorological station for the period from 1971 to The water balance is calculated on a monthly basis based on the strategy provided in Instructions and Tables for Computing Potential Evapotranspiration and the Water Balance (Thornthwaite and Mather, 1957). Site Specific: Tables 13 to 19 summarize the water balance calculations for the site. Enhanced LID infiltration structures as described in Section 6.4 are proposed to be installed throughout the proposed development to enhance ground water recharge. The total annual enhanced recharge volume available from the infiltration structures is 12,499 m 3 and is calculated by adding up the enhanced recharge volumes from Tables 13 and 16 (1,349 m ,150 m 2 = 12,499 m 3 ). The total annual natural recharge volume achieved from pervious surfaces is 7,437 m 3 and is calculated by adding up the recharge through pervious surface volumes from Tables 13 and 16 (3,113 m 3 + 4,325 m 3 = 7,437 m 3 ). Combining the enhanced recharge volume of 12,499 m 3 plus the natural recharge volume of 7,437 m 3 provides a total post-development on site annual infiltration volume of 19,937 m 3, which is 4.7% more than pre-development annual infiltration volume of 19,048 m 3 (see Table 19). The total post-development runoff volume from the site is 47,116 m 3. The pre-development runoff volume is 20,692 m 3. PAGE 22 OF 26

34 EXISTING CONDITION Contributing Catchments: 200 Soil Type: Clayey Sandy Silt Till Runoff Factor = 0.53 Contributing Area = 3.77 ha Vegetation: Shallow-rooted crops Evapotranspiration Percent Impervious = 2.70% Root Zone Depth = 0.5m Factor for Impervious Soil Moisture Retention Capacity = 75mm Surfaces = 0.34 Hart Subdivision City of Guelph Table 13 : Monthly Water Balance Wetland North of Harts Lane Month Daily Average Temperature Monthly Heat Index Unadjusted Daily Potential Evapotranspiration Correction Factors Adjusted Potential Evapotranspiration Average Precipitation P-PE Accum. Pot. Water Loss Storage S Pervious ET Actual Evapotranspiration Moisture Surplus Water Runoff Snow Melt Runoff Total Recharge & Runoff Actual Runoff ( C) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (m 3 ) (m 3 ) Jan Feb Mar Apr , May ,599 2,348 Jun ,317 1,191 Jul Aug Sep Oct Nov Dec Total ,842 7,087 POST-DEVELOPMENT CONDITION Contributing Catchments: 100, 101, 102 and Part of 200 Soil Type: Clayey Sandy Silt Till Runoff Factor = 0.75 Contributing Area = 2.48 ha Vegetation: Urban lawns Evapotranspiration Percent Impervious = 35.0% Root Zone Depth = 0.5m Factor for Impervious Soil Moisture Retention Capacity = 75mm Surfaces = 0.34 Month Daily Average Temperature Monthly Heat Index Unadjusted Daily Potential Evapotranspiration Correction Factors Adjusted Potential Evapotranspiration Average Precipitation P-PE Accum. Pot. Water Loss Storage S Pervious ET ( C) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (m 3 ) (m 3 ) (m 3 ) (m 3 ) (m 3 ) (m 3 ) (m 3 ) Jan Feb Mar Apr ,017 1, May ,375 2,798 5, ,119 Jun ,297 1,847 3, Jul ,463 2, Aug ,234 1, Sep , Oct Nov ,042 1, Dec Total ,654 1,349 8,192 12,014 20,206 3,113 4,462 Actual Evapotranspiration Notes: Precipitation and Temperature data from Environment Canada Climate Normals for the Guelph Arboretum Monthly water balance strategy as outlined in the document Instructions and Tables for Computing Potential Evapotranspiration and the Water Balance (Thornthwaite and Mather, 1957) Moisture Surplus Water Runoff Snow Melt Runoff Total Recharge & Runoff Total Recharge & Runoff Runoff Volume Total Enhanced Recharge (Table 15) Recharge Volume Runoff Volume Runoff Volume from South Total Runoff Volume North Recharge Through Pervious Surfaces Total Recharge Volume

35 Hart Subdivision City of Guelph Table 14: Enhanced Infiltration Structure Data Sheet Catchment 101 Drainage Area (ha) Length (m) Width (m) Depth (m) Volume (m 3 ) Storage Volume Contact Area (m 2 ) Percolation Rate Draindown (hr) (m 3 ) (mm/hr) Draindown is calculated using MOE Equation 4.3 Where: A = contact area of the trench (m²) V = runoff volume to be infiltrated (m 3 ) P = percolation rate of surrounding native soil (mm/h) n = porosity of the storage media (0.3 for clear stone) t = retention time hours)

36 Hart Subdivision Area of Enhanced Recharge ha (Part of Catchment 100) City of Guelph Recharge Time hours / 6.14 days Table 15 : Enhanced Recharge Calculation Recharge Volume Potential m 3 Infiltration Structures Wetland North of Harts Lane Month Total Recharge & Runoff (Table 13) No. of days Max Potential Recharge Available Recharge Total Enhanced Recharge (mm) (m 3 ) (m 3 ) (m 3 ) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total ,053 1,505 1,349

37 EXISTING CONDITION Contributing Catchments: 300 Soil Type: Clayey Sandy Silt Till Runoff Factor = 0.52 Contributing Area = 6.31 ha Vegetation: Shallow-rooted crops Evapotranspiration Percent Impervious = 1.90% Root Zone Depth = 0.5m Factor for Impervious Soil Moisture Retention Capacity = 75mm Surfaces = 0.34 Hart Subdivision City of Guelph Table 16 : Monthly Water Balance Wetland South of Harts Lane Month Daily Average Temperature Monthly Heat Index Unadjusted Daily Potential Evapotranspiration Correction Factors Adjusted Potential Evapotranspiration Average Precipitation P-PE Accum. Pot. Water Loss Storage S Pervious ET Actual Evapotranspiration Moisture Surplus Water Runoff Snow Melt Runoff Total Recharge & Runoff Actual Runoff ( C) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (m 3 ) (m 3 ) Jan Feb Mar Apr ,671 1,555 May ,281 3,984 Jun ,161 2,012 Jul ,103 1,027 Aug Sep Oct Nov ,346 1,253 Dec Total ,850 11,960 POST-DEVELOPMENT CONDITION Contributing Catchments:Part of 200 Soil Type: Clayey Sandy Silt Till Runoff Factor = 0.92 Diversion to North = 31% Contributing Area = 8.45 ha Vegetation: Urban lawns Evapotranspiration Percent Impervious = 73.0% Root Zone Depth = 0.5m Factor for Impervious Soil Moisture Retention Capacity = 75mm Surfaces = 0.34 Month Daily Average Temperature Monthly Heat Index Unadjusted Daily Potential Evapotranspiration Correction Factors Adjusted Potential Evapotranspiration Average Precipitation P-PE Accum. Pot. Water Loss Storage S Pervious ET ( C) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (m 3 ) (m 3 ) (m 3 ) (m 3 ) (m 3 ) (m 3 ) (m 3 ) Jan Feb Mar Apr ,294 1,017 2, ,625 May ,067 2,798 6,268 1,023 3,800 Jun ,985 1,847 4, ,545 Jul ,742 1,463 3, ,732 Aug ,997 1,234 2, ,294 Sep , , Oct , , Nov ,377 1,042 2, ,495 Dec , , Total ,399 11,150 38,924 12,014 26,910 4,325 15,475 Actual Evapotranspiration Notes: Precipitation and Temperature data from Environment Canada Climate Normals for the Guelph Arboretum Monthly water balance strategy as outlined in the document Instructions and Tables for Computing Potential Evapotranspiration and the Water Balance (Thornthwaite and Mather, 1957) Moisture Surplus Water Runoff Snow Melt Runoff Total Recharge & Runoff Total Recharge & Runoff Runoff Volume Total Enhanced Recharge (Table 18) Recharge Volume Total Runoff Volume Runoff Volume Diverted to North Total Runoff Volume South Recharge Through Pervious Surfaces Total Recharge Volume